German utility model No. 73 04 892 discloses a 4/2 directional control valve. Said valve uses a valve body which can be moved or actuated by an actuating spool because the closing spool is not guided directly within the sleeve which forms the seat. An offset situation can occur between the two conical seat-closing surfaces. Moreover, the minimum play required between the seat inner diameter and the dampening rod is larger than in a situation where the spool is directly guided within the seat portion. Therefore, the positive overlap is less effective in the annular gap thus formed and the amount of pressure medium passing through during the switching operation is larger, a situation which is particularly disadvantageous if the pressure medium is water.
A pilot-controlled poppet valve having two seats within the pump port chamber of the valve housing is already known. A spool, also having two seats, is reciprocally mounted between said two housing seats. Said movement occurs against the force of the pressure medium acting on the spool. For said purpose the spool is provided at its two opposite ends with differently sized pressure areas such that depending on the position of the pilot-controlled valve the spool is moved into the one or the other direction. This valve is of a complicated design. Specifically, the spool tends to tilt and does not operate precisely, a situation which will be particularly disadvantageous for water as the pressure medium.
It is also known to realize a pilot-controlled 3/2 poppet valve by means of so-called logic valves. This design will be discussed in some detail below. A disadvantage of this known design is the fact that the pilot valve has to be designed as a 4/2 directional valve, a fact which causes a doubling of cost because it has to be provided as a poppet valve.
It is an object of the invention to overcome the disadvantages of the prior art.
It is another object of the invention to provide a pilot-controlled 3/2 directional valve which can be manufactured at low cost. A still further object of the invention is to provide a pilot-controlled 3/2 directional poppet valve which can easily be assembled and operates with high precision. It is another object of the invention to provide the 3/2 directional valve such that standardized components can be used.